The present invention relates to isokinetic measurements and, in particular, it concerns a system and method for deriving angular isokinetic measurements using a linear dynamometer.
Muscle strength, which is the main parameter for estimation of muscle performance, can be measured in the context of two types of contraction: static and dynamic. During static contraction, the muscle does not move the joint since the external resistance matches the moment generated by the muscle. A value for muscle strength can thus, in principle, be obtained simply by using a load cell to measure this resistance. In practice, this approach is rarely used since the resulting value relates only to an isolated point in the range of motion and does not allow other important parameters to be determined.
Instead, the accepted technology for muscle strength determination employs isokinetic angular dynamometers which measure the moment exerted by a muscle during motion at a constant angular rate. Measurement of dynamic muscle strength has become one of the most important components in functional evaluation of patients primarily in the fields of orthopedics, rehabilitation and physiotherapy. Such measurements have also become very important for evaluation of damages and compensation in personal injury legal cases.
Devices for isokinetic exercise and therapy have been in use for many years. An early example is U.S. Pat. No. 3,465,592 to Perrine which discloses an isokinetic exercise system for both extension and flexion of a joint.
U.S. Pat. No. 4,235,437 to Ruis et al. discloses a robotic exercise machine which uses a computer to regulate the motion of an exercise arm in response to software programmed into the machine and in response to the force applied to the arm by the user as detected by a strain gauge at the end of the arm. By means of hydraulic cylinders and solenoid controlled valves, movement of the arm can be accurately controlled. However, the equipment provided in U.S. Pat. No. 4,235,437 is relatively complicated and requires expensive computer equipment and a complex linkage system. Further, because the equipment is computer controlled, the user must spend some time programming the computer with the desired settings before exercising. This, of course, is time consuming and detracts from the exercising.
It is to be appreciated that, with muscle exercise and rehabilitation apparatus, it is necessary that movement of the arm be smooth in all modes of operation. A problem with computer controlled apparatus is that the computer must make various samplings and computations, and thereafter makes corrections that are necessary. Although computer time is generally considered fast, the amount of time necessary for the computer to perform such operations and then control the mechanical and hydraulic devices of the apparatus may not result in smooth movement of the exercise arm, particularly at small loads.
Further, with hydraulic systems, such as that shown in the above U.S. patent, various problems of leakage, dirt in the servo valves, compliance in the hoses and pipes and heat dissipation result which detract from the accuracy of the system.
Representative of more modern systems currently in widespread use is U.S. Pat. No. 4,628,910 to Krukowski (Biodex Corp.). Such systems provide accurate measurements for concentric, and in some cases also eccentric, movements for a range of different joints. The complexity of the systems render them bulky and very costly.
The systems in widespread use typically take measurements over substantially the full range of mobility of the joint in question. Recently, research has indicated that measurements taken over a relatively small angular range in fact give results very similar to those taken over larger angular ranges. Examples of articles indicative of this finding include: Dvir Z., Keating J., The reproducibility of isokinetic trunk extension: A study using very short range of motion. Clinical Biomechanics 16:627-630, 2001; and Dvir Z., Steinfeld-Cohen, Y., Peretz, C., The identification of feigned isokinetic shoulder flexion weakness in normal subjects. American Journal of Physical Medicine and Rehabilitation 81:187-193, 2002. These findings have not previously been used to in any way simplify the measurement systems in use.
Finally, it should be noted that various implementations of linear dynamometers, including linear isokinetic dynamometers, have been developed. These linear dynamometers are typically used in devices for highly specific exercises, such as push-pull motions (e.g., U.S. Pat. No. 4,890,495), pedaling motions (e.g., U.S. Pat. No. 5,330,397) or lifting (e.g., U.S. Pat. No. 5,186,695). None of these devices are able to measure the angular isokinetic measurements which are required for muscle strength evaluations as described above.
There is therefore a need for a system and method for deriving angular isokinetic measurements which would be rendered simpler and more economical by employing a relatively small range of motion. It would also be advantageous to provide a system and method for deriving angular isokinetic measurements using a linear dynamometer.
The present invention is a system and method for deriving angular isokinetic measurements using a linear dynamometer.
According to the teachings of the present invention there is provided, a method for deriving isokinetic measurements of the moment applied by a body portion while the body portion performs a pivotal or flexing motion at a given angular velocity, the motion having an effective pivot axis, the method comprising: (a) providing a linear dynamometer configured for performing isokinetic measurements over a predefined range of motion along a linear path; (b) deploying the linear dynamometer for measuring force applied by the body portion, the dynamometer being positioned with its linear path substantially tangential to a circle of given radius about the effective pivot axis; (c) measuring by use of the linear dynamometer a force profile applied by the body portion over a predefined range of motion at a predefined linear velocity; and (d) using the force profile, the linear velocity and the radius to derive data for the moment applied by the body portion and the corresponding angular velocity.
According to a further feature of the present invention, the measuring is performed concentrically. According to an alternative, or additional, feature of the present invention, the measuring is performed eccentrically.
According to a further feature of the present invention, the measuring is performed at two different linear velocities, corresponding to two different angular velocities of the body portion about the effective pivot axis.
According to a further feature of the present invention, the predefined range of motion and the radius are chosen such that a corresponding range of angular motion of the body portion is less than 30xc2x0, and preferably no more than about 20xc2x0.
The method of claim 1, wherein the predefined range of motion is at least about 25 mm, and preferably between about 5 cm and about 15 cm.
There is also provided according to the teachings of the present invention, a system for deriving isokinetic measurements of the moment applied by a body portion of a subject while the body portion performs a pivotal or flexing motion at a given angular velocity, the motion having an effective pivot axis, the system comprising: (a) a linear dynamometer having a housing and a displacement portion, the linear dynamometer being configured for measuring a force applied to the displacement portion along a line of action while the displacement portion undergoes isokinetic linear motion along the line of action relative to the housing; (b) a chair for supporting the subject in a predefined position; and (c) an adjustable support system for supporting the linear dynamometer and the chair, the adjustable support system being configured to allow selective fixing of the linear dynamometer at any of a plurality of vertical positions over a given range of vertical displacement relative to the chair, and at any of a plurality of angular positions within a given range of angular positions about a substantially horizontal adjustment axis.
According to a further feature of the present invention, the adjustable support system is further configured to allow selective fixing of relative positions of the linear dynamometer and the chair within a predefined range of relative displacement in two degrees of freedom of horizontal displacement.
According to a further feature of the present invention, the predefined range of relative displacement in two degrees of freedom of horizontal displacement is defined by a system of rails supporting the chair.
According to a further feature of the present invention, the adjustable support system is further configured to allow rotation of the chair about a substantially vertical axis passing through the chair.
According to a further feature of the present invention, the adjustable support system is further configured to allow tilting of the chair about a substantially horizontal axis.